1. Field of the Invention
The present invention relates to a flexible wire grid polarizer used in a visible ray band and a fabricating method thereof.
2. Discussion of the Related Art
Generally, an array of parallel conductive wires arranged in parallel to polarize a specific polarized light has been used about 110 years. Such a parallel conductive wire array is called a wire grid in general. And, the wire grid is used on a transparent substrate as a polarizer in an infrared area among electromagnetic waves.
Major factors of determining polarizer performance of the wire grid are parallel lines and a distance between centers of the parallel lines, i.e., a relation between a cycle and a wavelength of an incident wave.
If an interval of a wire grid or a cycle is longer than a wavelength of an incident wave, the wire grid operative as a diffraction grid rather than a polarizer to diffract a polarized light. Hence, diffraction occurs regardless of the polarized light to form theoretically well-known diffraction interference patterns attributed to the phase difference.
If the difference between centers of lines or cycle is shorter than a wavelength, the wire grid is operative as a polarizer to reflect an electromagnetic wave polarized in parallel to the wire grid or to transmit the electromagnetic wave of orthogonal polarization. In this case, a transmissive area, in which a cycle of the wire grid lies within a range of 0.5*wavelength ˜2*wavelength, depends on variations of transmission and reflection characteristics of the wire grid.
Specifically, a rapid increase of reflectivity for an orthogonally polarized light to the wire grid and a corresponding transmitivity decrease take place on at least one specific wavelength in a predefined incident angle.
Meanwhile, cycle, line width, line thickness, property of grid material, characteristic of substrate (refractive index), wavelength of incident wave, incident angle of incident wave and the like are taken into consideration as important factors in manufacturing a polarized beam splitter using a wire grid.
It has been well known that metal wires arranged parallel in the aforesaid manner selectively reflect or transmit a polarized light of electromagnetic wave. If a cycle of the metal wire arrangement is shorter than a wavelength of an incident electromagnetic wave, a polarized (S-wave) component parallel to the metal wires is reflected and a polarized (P-wave) component orthogonal to the metal wires is transmitted.
A light of S-polarization, which has a polarization vector orthogonal to an incident plane, is parallel to a conductive factor. And, a light of P-polarization, which has a polarization vector parallel to the incident plane, is orthogonal to the conductive factor. Using such a phenomenon, it is able to fabricate a planar polarizer having excellent polarization efficiency, high transmitivity and wide viewing angle. Such a device can be called a wire grid polarizer. The wire grid polarizer consists of a glass substrate and an aluminum grid of which cycle is set to 200 nm or less to be provided with a polarizing function in visible rays. Namely, the wire grid polarizer consists of several parallel conductive electrodes supported by the glass substrate.
The wire grid polarizer generally reflects light having an electric field vector parallel to a conductive wire of a grid and transmits light having an electric field vector orthogonal to the conductive wire. In this case, an incident plane may be orthogonal to the wire grid or may not.
Ideally, the wire grid is a perfect mirror like S-polarization for one light polarization and is perfectly transparent for another polarization like P-polarization. Substantially, a mirror-like reflective metal absorbs a small quantity of incident angle and reflects about 90˜95%, whereas a plane mirror does not transmit 100% of incident light due to surface reflection.
FIGS. 1 to 8 are cross-sectional diagrams of a process of fabricating a wire grid polarizer according to a related art. A transparent glass substrate 100, as shown in FIG. 1, is prepared. In this case, both sides of the transparent glass substrate 100 are grinded. A thin metal layer 111 is deposited on the prepared glass substrate 100. In this case, Al, Ag, Cr or the like can be used as the thin metal layer 111.
After the thin metal layer 111 has been coated on the glass substrate 100, a polymer 121, as shown in FIG. 3, is coated on the thin metal layer 111. By pressurizing the polymer 121 with a prepared mold 130, a pattern 131 of the mold 130 is transcribed to the polymer 121. In this case, if the polymer 121 is a thermo-hardening material, a metal mold is used. If the polymer 12 is a UV-hardening material, a transparent polymer mold is used.
Once the pattern of the mold 130 is transcribed to the polymer 121, the mold 130, as shown in FIG. 4, is placed parallel to the polymer 121 after the polymer 121 has been coated on the thin metal layer 111. Heat or UV-ray is then applied to the mold 130 to harden the polymer 121. Namely, if the polymer 212 is the thermo-hardening material, the polymer is hardened by hot stamping. If the polymer is the UV-hardening material, a transparent mold is used by UV stamping instead of hardening the coated polymer.
After the polymer 121 has been hardened, the mold 130, as shown in FIG. 5, is separated from the polymer 122. Hence, a pattern 122 identical to the pattern 131 of the mold 130 is transcribed to the polymer 121 from which the mol 130 has been removed. In this case, tops and bottoms of the pattern 122 are opposite to those of the pattern 131 of the mold 130. In case of using hot stamping, the mold 130 is separated from the polymer 121 after a temperature of the substrate has been lowered. In case using UV stamping, the mold 130 is separated from the polymer 122 after completion of UV hardening.
After the mold 130 has been separated from the polymer 121, dry etch is carried out on an entire surface of the polymer pattern to expose a surface of the thin metal layer, as shown in FIG. 6, is exposed. Since prominence and depression is formed on the dry-etched polymer 121 by the mold 130 to have a step difference, the thin polymer is removed by the etch process to expose the surface of the thin metal layer.
Once the dry-etched polymer 123 is formed, a metal grid pattern 112, as shown in FIG. 7, is formed by etching the exposed thin metal layer 111 by dry or wet etch.
Subsequently, the polymer 123 remaining on the metal grid pattern 112 is removed to complete the wire grid polarizer, as shown in FIG. 8, having the specific metal grid pattern 112 on the substrate 100.
However, since the related art wire grid polarizer is fabricated on the glass substrate by a general semiconductor fabricating process, it is difficult to use the glass substrate that is thin.
And, the glass substrate is not fit for lightweight and duration.
Moreover, in case of a polarizing device having flexibility such as a flexible display and the like, it is unable to use the wire grid polarizer fabricated on the glass substrate.